Wind Load Calculator

This wind load calculator will show you how much force wind exerts on your structure at a specific velocity, helping you build roofs, windows, and signs safely.

Drag force16.1241 kN1,240.31 Pa dynamic pressure × 1.3 × 10 m²

Dynamic pressure ½ρv²1.2403 kPa

Power to overcome drag725.5828 kW973.02 hp — power goes as the CUBE of speed, because force goes as the square and power is force times speed

Drag area (C_d × A)13 m²the product is what matters — this is the figure to compare between vehicles

At 0.5× the speed4.031 kN0.25× the drag and 0.125× the power

At 1.5× the speed36.2791 kN2.25× the drag and 3.375× the power

At 2× the speed64.4963 kN4× the drag and 8× the power

Reference area conventionmust match the coefficienta car's C_d uses frontal area, a wing's uses plan area, and a sphere's uses its cross-section — mixing a coefficient with the wrong area is the commonest error here

The formula

F = ½ρv²C_dA for drag, ½ρv²C_lA for lift

Force squares, power cubes

Drag is dynamic pressure times a coefficient times a reference area. Because dynamic pressure goes as the square of speed, the force quadruples when the speed doubles — and since power is force times speed, the power required goes up eightfold.

That cube law is why top speed is so expensive and why efficient cruising is slow. A car needing 20 hp at 60 mph needs about 160 hp at 120 mph on drag alone, and it is why the last few miles per hour of a vehicle's top speed consume a disproportionate share of its engine.

The coefficient is meaningless without knowing which area it was defined against. Automotive drag coefficients use frontal area, aerofoil coefficients use plan area, and a sphere's uses its cross-section. This is why the drag area — the product of coefficient and area — is the honest figure for comparing vehicles: a low coefficient on a large frontal area is not aerodynamic.

Both coefficients vary with Reynolds number, sometimes sharply. A sphere's drag coefficient drops abruptly at around Re = 3 × 10⁵ when its boundary layer turns turbulent, which is exactly why golf balls have dimples.